In the use of laser oscillators as active sensing devices for illuminating an area or field of view containing a target of interest, the range of detection has been sought to be extended by the use of arrays of pluralities of laser oscillators and also by the phase-locking or slaving of the frequency and phase of such oscillators to that of a reference laser oscillator, as disclosed more fully in my co-pending U.S. Pat. Application Ser. No. 758,626 filed Jan. 12, 1977 for Phase-locking of Independent Laser Oscillators, now U.S. Pat. No. 4,096,448.
The range resolution of an active or ranging detection system or laser type radar is normally limited by the pulsewidth of the transmitted energy, as to limit the ability of an operator or observer to distinguish a point source reflector or discrete cultured target from amid the clutter background in which it occurs. Such limitation and means for overcoming such limitation are described in terms of a microwave radar system in U.S. Pat. No. 3,745,578 issued to Carl R. Barrett et al for "Multiple Frequency Radar System Having Improved Response to Small Targets". Such technique involves the generation of a coherent pulse train within a pulse-width modulation interval by means of an RF oscillator (f.sub.o) and IF spacing oscillator (f.sub.m) in bandpass-limited closed-loop cooperation with single sideband modulation means. RF power amplification and the pulsewidth modulation (or switching) of the coherent pulse train is provided by a pulse-modulated RF amplifier output stage. In other words, the mutually coherent multiple frequencies (f.sub.o +f.sub.m). . . (f.sub.o +nf.sub.m) giving rise to the coherent pulse train are generated by two (low power) RF oscillators in a bandpass-limited closed-loop radio frequency mixing arrangement, while the power output achieved is limited to that provided by the single RF power output stage.
None of such prior art arrangements teach the generation of laser pulse trains by the use of a plurality of mutually coherent laser frequencies. Nor does such art teach the combining of a plurality of laser oscillators with the use of mutually coherent multiple laser frequencies in order to combine improved system resolution and greater range performance.